SpringMVC中的HandlerAdapter适配器
什么是适配器模式
定义：将一个系统的接口转换成另外一种形式，从而使原来不能直接调用的接口变得可以调用。
适配器模式应用场景
- Mybatis多种日志框架的整合
- SpringMVC适配器模式
- 新老版本的兼容问题
SpringMVC适配器模式源码分析
1、通过URL找到具体的请求方法
mappedHandler = this.getHandler(processedRequest);
2、使用getHandlerAdapter获取对应的hanlder的具体HandlerAdapter,然后通过具体的适配器执行方法
HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());
在这里进行初始化三个适配器
先走父类
返回true
protected boolean supportsInternal(HandlerMethod handlerMethod) { return true; }
拿到对应的适配器
HandlerAdapter接口看下所有适配器类型
下面看下这几种适配器：
AbstractHandlerMethodAdapter implements HandlerAdapter
public final boolean supports(Object handler) { return handler instanceof HandlerMethod && this.supportsInternal((HandlerMethod)handler); }
HttpRequestHandlerAdapter implements HandlerAdapter
public boolean supports(Object handler) { return handler instanceof HttpRequestHandler; }
RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
protected boolean supportsInternal(HandlerMethod handlerMethod) { return true; }
SimpleControllerHandlerAdapter implements HandlerAdapter
public boolean supports(Object handler) { return handler instanceof Controller; }
SimpleServletHandlerAdapter implements HandlerAdapter
public boolean supports(Object handler) { return handler instanceof Servlet; }
- 继承Controller方式所使用的适配器：SimpleControllerHandlerAdapter
- HTTP请求处理器适配器：HttpRequestHandlerAdapter
- 注解方式（@Controller）的处理器适配器：RequestMappingHandlerAdapter
如果不采用适配器的话
If(hanlder instanceof Controller){
// 执行Controller适配器
}
If(hanlder instanceof HttpControler){
// 执行我们的HttpController
}
If(hanlder instanceof ServletControler){
// 执行我们的HttpController
}
If(hanlder instanceof AnnotationControler){
// 执行我们的AnnotationController
}
简单实现接口
@Controller("/httpRequestHandler")
public class ExtHttpRequestHandlerAdapter implements HttpRequestHandler {
@Override
public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("httpRequestHandler");
}
}
这个时候就会执行到HttpRequestHandlerAdapter适配器
模拟SpringMVC适配器模式
HandlerAdapter
public interface HandlerAdapter { /** * 根据hanlder判断是那个HandlerAdapter类型 如果找到对应的类型话返回true */ boolean supports(Object handler); /** * 执行我们的请求方法 */ void handle(Object handler); }
HandlerAdapter子类
public class AnnotationHandlerAdapter implements HandlerAdapter { /** * 注解形式的适配器 */ public boolean supports(Object handler) { return (handler instanceof AnnotationController); }
public void handle(Object handler) {
((AnnotationController) handler).hanlder();
}
}
public class HttpRequestHandlerAdapter implements HandlerAdapter { /** * Http类型 适配器 */ public boolean supports(Object handler) { return (handler instanceof HttpController); }
public void handle(Object handler) {
((HttpController) handler).hanlder();
}
}
Controller
public interface Controller {
**//请求方法**
void hanlder();
}
Controller子类
public class AnnotationController implements Controller { public void hanlder() { System.out.println("AnnotationController"); } }
public class HttpController implements Controller { public void hanlder() { System.out.println("HttpController"); } }
DispatcherServlet
public class DispatcherServlet {
private List
public DispatcherServlet() {
handlerAdapters = new ArrayList<HandlerAdapter>();
handlerAdapters.add(new HttpRequestHandlerAdapter());
handlerAdapters.add(new AnnotationHandlerAdapter());
}
public void dispatcher() {
**// 1. 已经获取到hanlder**
AnnotationController hanlder = new AnnotationController();
**// 2.获取具体适配器**
HandlerAdapter handlerAdapter = getHandlerAdapter(hanlder);
**// 3.执行我们的请求方案**
handlerAdapter.handle(hanlder);
}
public HandlerAdapter getHandlerAdapter(Controller controller) {
if (this.handlerAdapters != null) {
for (HandlerAdapter ha : this.handlerAdapters) {
if (ha.supports(controller)) {
return ha;
}
}
}
return null;
}
public static void main(String\[\] args) {
new DispatcherServlet().dispatcher();
}
}
本文参考：
蚂蚁课堂
